Surface-treated aluminum material and zinc-supplemented aluminum alloy

ABSTRACT

Provided are a surface-treated aluminum material having, on an aluminum material formed of aluminum or an aluminum alloy, a porous anodically oxidized film of a uniformly porous type exhibiting no visually recognizable crystal grain pattern after anodic oxidation treatment, and a novel zinc-doped aluminum alloy suitable for manufacture of the surface-treated aluminum material. The surface-treated aluminum material includes an aluminum alloy base material and an anodically oxidized film formed on a surface thereof, in which the aluminum alloy base material is formed of a zinc-doped aluminum alloy having an alloy composition containing 0.05 mass % to 1 mass % of a Zn component, 0.02 mass % or less of inevitable impurities, and the balance of aluminum.

TECHNICAL FIELD

The present invention relates to a surface-treated aluminum material having an anodically oxidized film on its surface and a zinc-doped aluminum alloy for manufacture of the surface-treated aluminum material, and more particularly, to a surface-treated aluminum material in which manifestation of a crystal grain pattern through anodic oxidation treatment is suppressed.

BACKGROUND ART

For an aluminum material formed of aluminum or an aluminum alloy, anodic oxidation treatment involving energizing the aluminum material as an anode in an electrolyte solution to form a film of aluminum oxide (Al₂O₃) (anodically oxidized film) on its surface is widely and generally performed in order to impart corrosion resistance, wear resistance, aesthetic appearance, functionality, and the like, because aluminum itself is liable to be corroded by, for example, an acid or an alkali. In addition, for example, in the anodic oxidation treatment using an aqueous solution of an acid, such as oxalic acid, sulfuric acid, or phosphoric acid, as an electrolyte, an anodically oxidized film called a porous-type film is formed through the anodic oxidation treatment. The porous-type film is formed of an inner-side (aluminum-side) dense film called a barrier layer, and a porous film called a porous layer, which is formed on an outer side of the barrier layer and has a large number of pores. At an initial stage of the anodic oxidation treatment, the barrier layer in accordance with a treatment voltage is first produced. After that, the large number of pores are generated in the barrier layer, and the large number of pores grow to form the porous layer.

Incidentally, examples of the aluminum material include a pure aluminum-based material (1000 series) and aluminum alloys, such as an Al—Cu-based alloy (2000 series), an Al—Mn-based alloy (3000 series), an Al—Si-based alloy (4000 series), and an Al—Mg-based alloy (5000 series). An aluminum alloy having its strength or workability improved by doping aluminum with another metal is widely used in industry. However, a high-purity aluminum material having high aluminum purity (Al purity) has an advantage, as compared to a general-purpose aluminum alloy, in that the influence of, for example, a second phase compound or inclusion responsible for a defect in its surface can be significantly reduced in various treatments, such as chemical dissolution treatment, electropolishing treatment, and anodic oxidation treatment, to be performed after work such as extrusion work or cutting work. Recently, development of products each obtained by working the high-purity aluminum material has been performed more actively in, for example, the following applications: housing members, such as doorknobs and fences; bicycle members, such as handlebars and cranks; vehicle members, such as entrance door frames and inner panels; decorative members, such as accessories and timepieces; optical product members, such as reflecting mirrors and cameras; and printing rolls.

Meanwhile, the aluminum material generally has a pattern (crystal grain pattern) resulting from crystal grains present in the material. In addition, the crystal grain pattern cannot be visually recognized with the naked eye before the anodic oxidation treatment but is manifested through the anodic oxidation treatment mainly owing to a difference in orientation between the crystal grains. Further, as the aluminum material has higher Al purity, the crystal grain size tends to be increased and the crystal grain pattern is more manifested through the anodic oxidation treatment. Particularly in the high-purity aluminum material, the crystal grains may have sizes as large as several hundreds of μm or more, and may have sizes of several mm depending on heat treatment.

In addition, the problem of the manifestation of such crystal grain pattern occurs also when the aluminum material has its surface subjected to planarization treatment by, for example, buff polishing, electropolishing, chemical polishing, and cutting work, and a crystal grain pattern that has not been visually recognizable before the anodic oxidation treatment is manifested through the anodic oxidation treatment to prevent uniform external appearance from being obtained. Consequently, in some applications where uniformity of external appearance may be regarded as important, the external appearance may be judged as a failure.

In view of the foregoing, as a method of solving the problem of the manifestation of the crystal grain pattern through the anodic oxidation treatment, the following method is conceivable: during casting of the aluminum material before the anodic oxidation treatment, its cooling rate is controlled or work such as cold forging is performed, to thereby make smaller the size of each of the crystal grains present in the aluminum material than a visually recognizable size (about 100 μm), and thus the crystal grain pattern is made apparently inconspicuous. However, even when the size of each of the crystal grains in the aluminum material is reduced to less than 100 μm, if the crystal grains are aggregated to have a size of 100 μm or more, the problem of the manifestation of the crystal grains in the anodic oxidation treatment occurs.

In addition, a method of working aluminum is limited depending on products, and hence there is a limitation on the reduction in size of each of the crystal grains. Particularly when the aluminum material is a material having high Al purity, or when heat treatment is required in manufacture, it is technically difficult to reduce the size of each of the crystal grains to 100 μm or less. In addition, even if the size of each of the crystal grains can be reduced, when the crystal grains are aggregated in the aluminum material, the aggregated crystal grains appear like one large crystal grain in external appearance. Accordingly, it is difficult to obtain uniform external appearance.

Incidentally, there has heretofore been proposed a technology in which the crystal grain pattern to be manifested through the anodic oxidation treatment is recognized as external appearance having an excellent design and which involves purposely manifesting the crystal grain pattern in the aluminum material after the anodic oxidation treatment (see, for example, Patent Literature 1). However, there is found no example of development of a material in which the crystal grain pattern is hardly manifested after the anodic oxidation treatment.

CITATION LIST Patent Literature

[PTL 1] JP 06-287773 A

SUMMARY OF INVENTION Technical Problem

In view of the foregoing, the inventors of the present invention have first conducted detailed research and investigation on the cause of the manifestation of a crystal grain pattern through anodic oxidation treatment, and have ascertained that crystal grains having a difference in orientation differ from each other in shape at an aluminum metal (Al)/barrier layer (Al₂O₃) interface in an aluminum material after the anodic oxidation treatment. That is, in the anodic oxidation treatment, at the initial stage of film formation, a barrier layer is first formed, and then pores begin to open in the formed film. In this case, when the crystal grains have a difference in orientation, the difference in orientation between the crystal grains causes a difference in the generation of pores, and the resultant difference causes a slight difference to be formed in, for example, shape or unevenness between a large number of pores generated at the aluminum metal (Al)/barrier layer (Al₂O₃) interface. The formed slight difference between the large number of pores is also reflected in a porous layer to be formed through the subsequent growth of the large number of pores. In addition, even if the slight difference between the large number of pores in the anodically oxidized film thus formed is extremely small, the difference is highlighted and manifested as a crystal grain pattern when the surface is irradiated with light, to thereby cause a failure to form uniform external appearance in the aluminum material after the anodic oxidation treatment.

In addition, on the basis of the investigation results, the inventors of the present invention have made further investigation on a method of uniformizing the large number of pores to be generated at the aluminum metal (Al)/barrier layer (Al₂O₃) interface to the extent possible irrespective of the orientation of the crystal grains. As a result, the inventors have found the following. When a specific zinc-doped aluminum alloy having an alloy composition containing 0.05 mass % to 1 mass % of a Zn component, 0.02 mass % or less of inevitable impurities, and the balance of aluminum is used as an aluminum material, pores easily open at the initial stage of film formation. In addition, the pores begin to open in a uniform manner irrespective of the orientation of the crystal grains to enable the formation of a porous layer having pores of a uniform shape in the subsequent anodic oxidation treatment. As a result, a crystal grain pattern can be prevented to the extent possible from being manifested in the aluminum material after the anodic oxidation treatment and a uniform anodically oxidized film hardly having a defect can be formed. Thus, the present invention has been completed.

Therefore, an object of the present invention is to provide a surface-treated aluminum material having a porous anodically oxidized film of a uniformly porous type exhibiting no visually recognizable crystal grain pattern after anodic oxidation treatment.

Another object of the present invention is to provide a novel zinc-doped aluminum alloy suitable for manufacture of a surface-treated aluminum material having a porous anodically oxidized film of a uniformly porous type exhibiting no visually recognizable crystal grain pattern after anodic oxidation treatment.

Solution to Problem

That is, according to one embodiment of the present invention, there is provided a surface-treated aluminum material, including: an aluminum alloy base material; and an anodically oxidized film formed on a surface of the aluminum alloy base material, in which the aluminum alloy base material is formed of a zinc-doped aluminum alloy having an alloy composition containing 0.05 mass % to 1 mass % of a Zn component, 0.02 mass % or less of inevitable impurities, and the balance of aluminum.

According to another embodiment of the present invention, there is provided a zinc-doped aluminum alloy, which is obtained by doping high-purity aluminum with Zn, the zinc-doped aluminum alloy including 0.05 mass to 1 mass % of a Zn component, 0.02 mass % or less of inevitable impurities, and the balance of aluminum.

The surface-treated aluminum material of the present invention is obtained by the anodic oxidation treatment of the aluminum alloy base material formed of the zinc-doped aluminum alloy, and the zinc-doped aluminum alloy contains 0.05 mass or more and 1 mass % or less, preferably 0.25 mass % or more and 0.8 mass % or less of the Zn component, 0.02 mass % or less, preferably 0.01 mass % or less of the inevitable impurities except the Zn component, such as Si, Fe, Cu, Mn, Mg, Ti, Mg, and Ni, and the balance of aluminum.

In this connection, when the zinc-doped aluminum alloy contains less than 0.05 mass % of the Zn component, the orientation of the crystal grains causes a difference in the generation of pores, and the suppressing effect on the manifestation of a crystal grain pattern is difficult to exhibit. In contrast, when the zinc-doped aluminum alloy contains more than 1 mass % of the Zn component, the anodically oxidized film may be locally dissolved to cause a defect in the surface. In addition, when the zinc-doped aluminum alloy contains more than 0.02 mass % of the inevitable impurities except the Zn component, the local dissolution of the film due to second phase grains, the generation of a portion in which the film is not formed, or the like is more liable to occur than in a material having high Al purity, with the result that a uniform anodically oxidized film cannot be formed over a wide range. In particular, inevitable impurities each having an electropositive potential with respect to Al (e.g., Fe, Si, Cu, Ni, and Ti) may cause the local dissolution of the film through the anodic oxidation treatment, and hence it is desired that the zinc-doped aluminum alloy contain 0.01 mass % or less of those inevitable impurities.

In the present invention, the aluminum alloy base material may have its surface subjected to planarization treatment by, for example, cutting work, buff polishing, electropolishing, and chemical polishing. In addition, the shape of the aluminum alloy base material is also not particularly limited, and examples thereof may include wrought materials, such as a cast material, an extrusion material, a plate material, and a roll material. The present invention is particularly effective for an aluminum alloy base material subjected to planarization treatment because a crystal grain pattern is liable to be manifested therein through the anodic oxidation treatment.

A manufacturing method for the zinc-doped aluminum alloy to be used in the present invention is not particularly limited as long as the above-mentioned alloy composition of the zinc-doped aluminum alloy can be achieved, and a hitherto generally performed manufacturing method for an aluminum alloy may be applied. Examples thereof may include: a gravity casting method for manufacturing a cast material or the like through the use of, for example, a book mold or a boat-shaped die; a DC casting method for manufacturing, for example, a columnar billet or a slab having a rectangular parallelepiped shape; and a continuous casting method for manufacturing, for example, a plate-like ingot. In addition, as described later, when the steps of the manufacture of the aluminum alloy base material include a step of melting the aluminum alloy, the zinc-doped aluminum alloy having the predetermined alloy composition may be prepared by doping required Zn into high-purity aluminum in the melting step.

In addition, as a manufacturing method for the aluminum alloy base material to be used in the present invention, for example, there may be given: the above-mentioned gravity casting method for manufacturing a cast material; an extrusion method for obtaining an aluminum alloy wrought material having the shape of a rod, a roll, or the like through the use of a columnar billet obtained by the above-mentioned DC casting method; a hot or cold rolling method for obtaining a plate material through the use of a slab having a rectangular parallelepiped shape obtained by the above-mentioned DC casting method; and a cold rolling method for obtaining a plate or a foil through the use of a plate-like ingot obtained by the above-mentioned continuous casting method.

In the present invention, on the surface of the aluminum alloy base material formed of the above-mentioned zinc-doped aluminum alloy, the anodically oxidized film is formed through anodic oxidation treatment. In addition, the anodic oxidation treatment in this case is not particularly limited. However, in view of the fact that the present invention is particularly effective for a porous-type anodically oxidized film that is liable to manifest a crystal grain pattern, the anodic oxidation treatment is preferably anodic oxidation treatment using, as a treatment bath, a polybasic acid aqueous solution in which the porous-type anodically oxidized film is produced.

The polybasic acid aqueous solution to be used as the treatment bath in the anodic oxidation treatment for forming the porous-type anodically oxidized film is also not particularly limited. As a polybasic acid constituting the treatment bath, for example, there may be given mineral acids, such as sulfuric acid, phosphoric acid, and chromic acid, and organic acids, such as oxalic acid, tartaric acid, and malonic acid. The polybasic acid concentration of the treatment bath using any such polybasic acid (polybasic acid aqueous solution) may be similar to that used in general anodic oxidation treatment. For example, in the case of sulfuric acid, the polybasic acid concentration is 10 wt % or more and 20 wt % or less, preferably 14 wt % or more and 18 wt % or less.

In addition, the treatment conditions of the anodic oxidation treatment using the polybasic acid aqueous solution as the treatment bath are also not particularly limited, and may be similar to those adopted in general anodic oxidation treatment, in particular anodic oxidation treatment for forming a porous-type anodically oxidized film through the use of a polybasic acid aqueous solution as a treatment bath. For example, in the case of using sulfuric acid as the treatment bath, the treatment conditions are approximately as follows: a treatment bath temperature of 18° C., a treatment voltage of from 10 V to 15 V, and a film thickness of from 1 μm to 20 μm.

Advantageous Effects of Invention

The surface-treated aluminum material of the present invention has the anodically oxidized film formed on the surface of the aluminum alloy base material formed of the zinc-doped aluminum alloy having the specific alloy composition, and is excellent in uniformity of external appearance without the manifestation of a crystal grain pattern. In addition, the surface-treated aluminum material can be industrially easily manufactured, and is suitably used in applications where uniformity of external appearance is particularly regarded as important, such as housing members, bicycle members, vehicle members, decorative members, optical product members, construction product members, members of products for anodic oxidation, such as plates and rolls, and printing rolls.

DESCRIPTION OF EMBODIMENTS

Now, a suitable embodiment of the present invention is more specifically described on the basis of Examples and Comparative Examples.

Example 1

6.5 kg of high-purity aluminum having a purity of 99.99% was doped with 3.25 g of Zn having a purity of 99.9999%. The resultant was melted in a crucible for experimentation at 720° C., and was then cast into a book mold-type mold measuring 30 t×150 w×190 l that had been preheated to 150° C. by a gravity casting method to provide an aluminum alloy base material formed of a zinc-doped aluminum alloy of Example 1. The alloy composition of the resultant aluminum alloy base material was investigated by glow discharge mass spectrometry (GD-MS method; apparatus: Model VG9000 manufactured by VG Elemental) and was found to be as follows: Zn: 0.05%, Si: 0.003%, Fe: 0.001%, Cu: <0.001%, Mn: 0.001%, Mg: 0.003%, others: 0.002%, and Al: balance. The results are shown in Table 1.

Example 2

6.5 kg of high-purity aluminum having a purity of 99.99% was doped with 16.25 g of Zn having a purity of 99.9999%, and an aluminum alloy base material formed of a zinc-doped aluminum alloy of Example 2 was obtained by a similar method to that of Example 1. After that, its alloy composition was investigated. The results are shown in Table 1.

Example 3

6.5 kg of high-purity aluminum having a purity of 99.99% was doped with 32.50 g of Zn having a purity of 99.9999%, and an aluminum alloy base material formed of a zinc-doped aluminum alloy of Example 3 was obtained by a similar method to that of Example 1. After that, its alloy composition was investigated. The results are shown in Table 1.

Example 4

6.5 kg of high-purity aluminum having a purity of 99.99% was doped with 65.00 g of Zn having a purity of 99.9999%, and an aluminum alloy base material formed of a zinc-doped aluminum alloy of Example 4 was obtained by a similar method to that of Example 1. After that, its alloy composition was investigated. The results are shown in Table 1.

Example 5

6.5 kg of high-purity aluminum having a purity of 99.99% was doped with 65.00 g of Zn having a purity of 99.5%, and an aluminum alloy base material formed of a zinc-doped aluminum alloy of Example 5 was obtained by a similar method to that of Example 1. After that, its alloy composition was investigated. The results are shown in Table 1.

Comparative Example 1

6.5 kg of high-purity aluminum having a purity of 99.99% was doped with 0.65 g of Zn having a purity of 99.9999%. The resultant was melted in a crucible for experimentation at 720° C., and was then cast into a book mold-type mold measuring 30 t×150 w×190 l that had been preheated to 150° C. by a gravity casting method to provide an aluminum alloy base material formed of a zinc-doped aluminum alloy of Comparative Example 1. The alloy composition of the resultant aluminum alloy base material was investigated by glow discharge mass spectrometry (GD-MS method; apparatus: Model VG9000 manufactured by VG Elemental) and was found to be as follows: Zn: 0.01%, Si: 0.003%, Fe: 0.001%, Cu: <0.001%, Mn: 0.001%, Mg: 0.003%, others: 0.002%, and Al: balance. The results are shown in Table 1.

Comparative Example 2

6.5 kg of high-purity aluminum having a purity of 99.99% was doped with 130 g of Zn having a purity of 99.9999%, and an aluminum alloy base material formed of a zinc-doped aluminum alloy of Comparative Example 2 was obtained by a similar method to that of Comparative Example 1. After that, its alloy composition was investigated. The results are shown in Table 1.

Comparative Example 3

6.5 kg of high-purity aluminum having a purity of 99.95% was doped with 32.5 g of Zn having a purity of 99.9999%, and an aluminum alloy base material formed of a zinc-doped aluminum alloy of Comparative Example 3 was obtained by a similar method to that of Comparative Example 1. After that, its alloy composition was investigated. The results are shown in Table 1.

Comparative Examples 4 to 7

The following alloys were each used as an aluminum alloy for forming an aluminum alloy base material: a JIS A2024 alloy (Zn: 0.25, Si: 0.5, Fe: 0.5, Cu: 4, Mn: 0.35, Mg: 1.5, others: 0.1, balance: Al) was used in Comparative Example 4, a JIS A3003 alloy (Zn: 0.1, Si: 0.6, Fe: 0.7, Cu: 0.1, Mn: 1.2, Mg: <0.001, others: 0.1, balance: Al) was used in Comparative Example 5, a JIS A5052 alloy (Zn: 0.1, Si: 0.25, Fe: 0.4, Cu: 0.1, Mn: 0.1, Mg: 2.5, others: 0.006, balance: Al) was used in Comparative Example 6, and a JIS A6061 alloy (Zn: 0.25, Si: 0.5, Fe: 0.7, Cu: 0.2, Mn: 0.15, Mg: 0.2, others: 0.45, balance: Al) was used in Comparative Example 7.

Examples 6 to 26

An aluminum piece measuring 50 mm×50 mm×10 mm was cut out of each of the aluminum alloy base materials of Examples 1 to 5 shown in Table 2, and was subjected to planarization treatment so as to have a surface roughness Rt of <200 nm through buff polishing treatment. Thus, an aluminum piece (aluminum alloy base material) having a specular gloss was obtained.

The thus obtained aluminum piece having a specular gloss was subjected to anodic oxidation treatment using a polybasic acid aqueous solution and treatment conditions shown in Table 2, and was then washed with water and dried to provide an aluminum piece after anodic oxidation treatment (test piece: surface-treated aluminum material) of each of Examples 6 to 26.

[Evaluation of Crystal Grain Pattern by Surface Observation]

The test pieces obtained in Examples 6 to 26 were subjected to the following surface observation: a test piece having a crystal grain pattern visible in visual observation under a fluorescent lamp having an illuminance of 1,500 Lux or more and 2,500 Lux or less was evaluated as Symbol “x”; a test piece having no crystal grain pattern visible in visual observation under a fluorescent lamp having an illuminance of 1,500 Lux or more and 2,500 Lux or less was evaluated as Symbol “∘”; and a test piece having no crystal grain pattern visible in visual observation under a video light having an illuminance of 15,000 Lux or more and 20,000 Lux or less was evaluated as Symbol “⊚”. Thus, evaluation of the crystal grain pattern in each of the test pieces was performed.

The results are shown in Table 2.

[Evaluation of Anodically Oxidized Film by SEM Observation]

The test pieces obtained in Examples 6 to 26 were each observed with a scanning electron microscope (SEM) in the range of about 25 μm by about 25 μm (corresponding to a field of view at a magnification of about 5,000), and evaluation of an anodically oxidized film was performed by the following evaluation criteria: ⊚: a test piece in which the anodically oxidized film is uniform and free of any defect; ∘: a test piece in which one to ten defects in the anodically oxidized film each having a size of 5 μm or less are observed but no defect therein having a size of 5 μm or more is observed within the field of view; and x: a test piece in which ten or more defects in the anodically oxidized film each having a size of 5 μm or less are observed or one or more defects therein each having a size of 5 μm or more are observed within the field of view, or a test piece in which a uniform anodically oxidized film is not formed.

The results are shown in Table 2.

[Overall Evaluation]

The test pieces obtained in Examples 6 to 26 were subjected to overall evaluation by the following evaluation criteria: 0: a test piece evaluated as Symbol “⊚” or “∘” in both the “surface observation evaluation” and the “SEM observation evaluation”; and x: a test piece evaluated as Symbol “Δ” or “x” in any one of the “surface observation evaluation” and the “SEM observation evaluation.”

Comparative Examples 8 to 14

With the use of aluminum alloy base materials of Comparative Examples 1 to 7 shown in Table 3, comparative aluminum pieces (aluminum alloy base materials) of Comparative Examples 8 to 14 were prepared in the same manner as in the case of Examples 6 to 26 described above. Then, the resultant comparative aluminum pieces of Comparative Examples 8 to 14 were subjected to anodic oxidation treatment in a treatment bath of 2 wt % oxalic acid (20° C.) under the treatment conditions of a voltage of 40 V and an electrical quantity of 20 C/cm², and were then washed with water and dried to provide comparative aluminum pieces after anodic oxidation treatment (comparative test pieces: surface-treated aluminum materials) of Comparative Examples 8 to 14.

The resultant comparative test pieces of Comparative Examples 8 to 14 were subjected to the evaluation of the crystal grain pattern by surface observation, the evaluation of the anodically oxidized film by SEM observation, and the overall evaluation in the same manner as in the case of Examples described above.

The results are shown in Table 3.

TABLE 1 Alloy composition of Al alloy base material (%) Inevitable impurities Test Example No. Zn Si Fe Cu Mn Mg Others Total Al Example 1 0.05 0.003 0.001 <0.001 0.001 0.003 0.002 0.010 Balance 2 0.25 0.003 0.001 <0.001 0.001 0.003 0.002 0.010 Balance 3 0.50 0.003 0.001 <0.001 0.001 0.003 0.002 0.010 Balance 4 1.00 0.003 0.001 <0.001 0.001 0.003 0.002 0.010 Balance 5 1.00 0.003 0.001 <0.001 0.001 0.003 0.006 0.014 Balance Comparative 1 0.01 0.003 0.001 <0.001 0.001 0.003 0.002 0.010 Balance Example 2 2 0.003 0.001 <0.001 0.001 0.003 0.002 0.010 Balance 3 0.5 0.03 0.01 <0.001 0.001 0.003 0.006 0.050 Balance 4 0.25 0.5 0.5 4 0.35 1.5 0.1 6.950 Balance (A2024*¹⁾) 5 0.1 0.6 0.7 0.1 1.2 <0.001 0.1 2.700 Balance (A3003*¹⁾) 6 0.1 0.25 0.4 0.1 0.1 2.5 0.006 3.356 Balance (A5052*¹⁾) 7 0.25 0.5 0.7 0.2 0.15 0.2 0.45 2.200 Balance (A6061*¹⁾) (Note) ^(*1))Aluminum alloy No. based on the JIS standard

TABLE 2 Anodic oxidation treatment Al alloy Kind of electrolytic Electrical Evaluation Example base solution and treatment Voltage quantity Surface SEM No. material temperature (V) (C/cm²) observation observation Overall 6 Example 1 15 wt % sulfuric acid 15 20 ◯ ⊚ ◯ (18° C.) 7 2 wt % oxalic acid 40 20 ◯ ⊚ ◯ (20° C.) 8 0.5 wt % oxalic acid 90 20 ◯ ⊚ ◯ (10° C.) 9 4% wt phosphoric acid 40 20 ◯ ⊚ ◯ (25° C.) 10 4% wt phosphoric acid 60 20 ◯ ⊚ ◯ (20° C.) 11 Example 2 15 wt % sulfuric acid 15 20 ◯ ⊚ ◯ (18° C.) 12 2 wt % oxalic acid 40 20 ◯ ⊚ ◯ (20° C.) 13 0.5 wt % oxalic acid 90 20 ◯ ⊚ ◯ (10° C.) 14 4 wt % phosphoric acid 40 20 ◯ ⊚ ◯ (25° C.) 15 4 wt % phosphoric acid 60 20 ⊚ ⊚ ◯ (25° C.) 16 Example 3 15 wt % sulfuric acid 15 20 ⊚ ⊚ ◯ (18° C.) 17 2 wt % oxalic acid 40 20 ⊚ ⊚ ◯ (20° C.) 18 0.5 wt % oxalic acid 90 20 ⊚ ⊚ ◯ (10° C.) 19 4 wt % phosphoric acid 40 20 ⊚ ⊚ ◯ (25° C.) 20 4 wt % phosphoric acid 60 20 ⊚ ⊚ ◯ (25° C.) 21 Example 4 15 wt % sulfuric acid 15 20 ⊚ ⊚ ◯ (18° C.) 22 2 wt % oxalic acid 40 20 ⊚ ⊚ ◯ (20° C.) 23 0.5 wt % oxalic acid 90 20 ⊚ ⊚ ◯ (10° C.) 24 4 wt % phosphoric acid 40 20 ⊚ ⊚ ◯ (25° C.) 25 4 wt % phosphoric acid 60 20 ⊚ ⊚ ◯ (25° C.) 26 Example 5 15 wt % sulfuric acid 15 20 ◯ ◯ ◯ (18° C.)

TABLE 3 Anodic oxidation treatment Al alloy Kind of electrolytic Electrical Evaluation Comparative base solution and treatment Voltage quantity Surface SEM Example No. material temperature (V) (C/cm²) observation observation Overall 8 Comparative 2 wt % oxalic acid (20° C.) 40 20 x ∘ x Example 1 9 Comparative 2 wt % oxalic acid (20° C.) 40 20 Δ x x Example 2 10 Comparative 2 wt % oxalic acid (20° C.) 40 20 Δ x x Example 3 11 Comparative 2 wt % oxalic acid (20° C.) 40 20 x x x Example 4 12 Comparative 2 wt % oxalic acid (20° C.) 40 20 x x x Example 5 13 Comparative 2 wt % oxalic acid (20° C.) 40 20 x x x Example 6 14 Comparative 2 wt % oxalic acid (20° C.) 40 20 x x x Example 7 

1. A surface-treated aluminum material, comprising: an aluminum alloy base material; and an anodically oxidized film formed on a surface of the aluminum alloy base material, wherein the aluminum alloy base material is formed of a zinc-doped aluminum alloy having an alloy composition containing 0.05 mass % to 1 mass % of a Zn component, 0.02 mass % or less of inevitable impurities, and the balance of aluminum.
 2. A surface-treated aluminum material according to claim 1, wherein the anodically oxidized film is formed through anodic oxidation treatment using a polybasic acid aqueous solution as a treatment bath.
 3. A surface-treated aluminum material according to claim 1 or 2, wherein the aluminum alloy base material is subjected to planarization treatment by any one method selected from cutting work, buff polishing, electropolishing, and chemical polishing, prior to the anodic oxidation treatment.
 4. A zinc-doped aluminum alloy, which is obtained by doping high-purity aluminum with Zn, the zinc-doped aluminum alloy comprising 0.05 mass % to 1 mass % of a Zn component, 0.02 mass % or less of inevitable impurities, and the balance of aluminum. 